The invention relates generally to air conditioning systems suitable for residential and light commercial applications, and more particularly to solar-powered systems suitable for such applications.
The possibility of using solar energy to decrease the usage of electricity in air conditioning systems has been widely suggested. Of all the proposed technologies, solar-assisted air conditioning systems using absorption chillers have become one of the most appealing. Solar absorption cooling systems have been installed in different parts of the world to evaluate their feasibility and performance. These types of systems are described in:
Van Hattem, D., and Dato, P. A., Description and Performance of an Active Solar Cooling System, Using a LiBrxe2x80x94H2O Absorption Machine, Energy and Buildings, 1981, Vol. 3, pp. 169-196;
Yellot, J. I., Operation of an Active Solar Air-Conditioning System in a Hot, Dry Climate, ASHRAE, 1982, Vol 2;
Bong, T. Y., Ng, K. C., and Tay, A. O., Performance Study of a Solar-Powered Air Conditioning System, Solar Energy, 1987, Vol.39, No. 3, pp. 173-182;
Hernxc3xa1ndez, H., Analysis and Modeling of a Solar-Assisted Air Conditioning Dehumidification System for Applications in Puerto Rico, M.S. Thesis, University of Puerto Rico, 1997; and
Meza, J. I., Khan, A. Y., and Gonzalez, J. E., Experimental Assessment of a Solar Assisted Air Conditioning System for Applications in Puerto Rico, Solar Engineering, 1998, pp. 149-154.
Each of these references is incorporated herein by reference in their entirety.
These and related absorption systems are well known in the art. More generally, absorption is the process by which refrigerant vapor is absorbed to a concentrated solution. The heat of condensation of the water and the heat of mixing are released into the fluid by the absorption process. The fluid must be cooled to allow sufficient refrigerant to be continuously absorbed into solution while maintaining a low-pressure condition. Water and lithium-bromide have been widely used in these systems. This working fluid utilizes water as the refrigerant and is therefore limited to refrigeration temperatures above 0xc2x0 C. Absorption machines based on water and lithium-bromide are typically configured as water chillers for air-conditioning systems in large buildings. Typical machines are available in sizes ranging from 10 to 1500 tons.
These machines have a reputation for consistent, dependable service. Nonetheless, they also require a large amount of electricity to operate. Although the above-listed solar-powered systems have demonstrated the feasibility of reducing electricity usage, they have not become commercially available or widely used. A number of factors have contributed to this delay. For example, the last listed system uses a cooling tower to exhaust heat generated by the absorption chiller. While such industrial equipment is tolerable in heavy commercial settings, it is unsightly in residential or similar settings.
Likewise, the solar-powered systems have not been available in a package offering a compact design and dependable operation for residential or light-commercial applications.
According to one aspect of the invention, one preferred solar-powered air conditioning system includes an air-cooled single-effect absorption machine. A lithium-bromide solution is used as the absorbent and a water solution is used as the refrigerant. The absorption machine includes a desorber, condenser, an evaporator and an absorber. The components are selected to deliver a cooling load of three to five tons.
According to another aspect of the invention, a compact solar-powered air conditioning system operates without a cooling tower. The air conditioning system includes solar collectors, a storage tank, and an absorption machine. The solar collectors are positioned to collect energy and to heat water as it passes along a path through their interior. The heated water is passed to the storage tank. The heated water in the storage tank is used to drive the absorption machine, which includes a desorber, a condenser, an evaporator and an air-cooled absorber. The desorber receives the heated water and causes a refrigerant to change from a liquid state to a gaseous state. The condenser then receives the refrigerant in the gaseous state and causes the refrigerant to return to a liquid state. The evaporator then receives the refrigerant in the liquid state and returns the refrigerant to a gaseous state. This change from the liquid state to the gaseous state is able to absorb energy from an external cooling loop. Finally, the absorber then receives the refrigerant in the gaseous state circulates an absorbent solution in the presence of the refrigerant. The absorber releases heat of dilution and heat of condensation. This heat is exhausted by passing ambient air over the absorber.
According to further aspects of the invention, the solar collectors are connected in series and draw water from the storage tank through a manifold. The stratified storage tank draws the heated fluid to drive the refrigeration loop from a layer having a highest temperature. When its temperature is insufficient to drive the refrigeration loop, it is passed through a heater positioned between the storage tank and the absorption machine.
According to still further aspects of the invention, the absorption machine uses a water-based refrigerant and a lithium-bromide absorbent. The components of the absorption machine are housed within an enclosure. The enclosure defines a first air inlet and a first exhaust configured to permit the passage of ambient air through the housing and over the absorber. The enclosure also defines a second air inlet and a second exhaust configured to permit the passage of ambient air through the housing and over the condenser. The absorption machine is configured to deliver a cooling load ranging from three to five tons.
According to another aspect of the invention, a compact solar-powered air conditioning system includes solar collectors, a storage tank and an absorption machine. The solar collectors circulate water to collect energy, the heated water is passed to the storage tank. The absorption machine draws the heated water from the storage tank to drive a cooling circuit. The absorption machine includes an air-cooled condenser, an air cooled absorber and an enclosure. The air-cooled condenser extracts heat by changing the state of a refrigerant from a vapor to a liquid. The air-cooled absorber is coupled with the air-cooled condenser through an evaporator. The air-cooled absorber extracts heat by absorbing a vapor refrigerant in a liquid absorbent. The enclosure houses the air-cooled absorber, and the air-cooled condenser. The enclosure has a first air-flow path configured to pass ambient air across the air-cooled absorber. The enclosure has a second air-flow path configured to pass ambient air across the air-cooled condenser.
According to further aspects of the invention, a first duct through the enclosure defines the first air-flow path that begins with an intake aperture and terminates at an exhaust aperture. A second duct through the enclosure defines the second air-flow path that begins with an intake aperture and terminates at an exhaust aperture. The first and second ducts maintain the first air-flow path separate from the second air-flow path. The enclosure defines at least four distinct surfaces including a top, front, rear and side surface. The side defines the intake aperture and the front defines the exhaust aperture of the first duct. The rear defines the intake aperture and the top defines the exhaust aperture of the second duct. A fan is positioned at or in each duct to drive ambient air through the ducts.
According to a still further aspect of the invention, the air-cooled condenser and the air-cooled absorber are constructed of parallel copper tubes and aluminum fins. Air passes across the aluminum fins to exhaust heat from the components.
According to another aspect of the invention, a solar-powered air conditioning system is operated without a cooling tower. A fluid is drawn from a storage tank at a level having a lower temperature than other levels in the storage tank. The fluid is passed through solar collectors to increase its temperature and returned to the storage tank. The heated fluid is drawn from the storage tank at a level having a higher temperature than other levels of the storage tank. The heated fluid is passed though an air-cooled absorption machine. The energy from the heated fluid drives a cooling loop configured to extract energy from a building.
These and other aspects of the invention will be appreciated in greater detail with reference to the drawings and the detailed description that follows.